In order to sense an article concealed in a wall, for example a beam in a wall of lightweight construction, capacitive detectors are known. Such detectors use an electrode that has its charging or discharge behavior determined in order to infer the dielectric object. Detectors having a plurality of electrodes are also known, which involve determining a change in the capacitance of a pair of electrodes. Usually, it is necessary for such detectors to be calibrated manually on the wall, since the appliances cannot detect wall contact themselves and the capacitance of the electrodes or electrode pairs is dependent on ambient conditions, such as a temperature, a humidity, an object averted from the sensor, grounding via a user or electrical or dielectric properties of the wall material. In order to take account of these variable influencing factors, it is necessary for known appliances to be calibrated on the wall, which requires either appropriate control by a user or a complex sensor system.
DE 10 2007 058 088 A1 shows a sensor for locating dielectric objects in a medium. The sensor shown determines a ratio between a reference capacitance and a measurement capacitance, the latter being dependent on the position of the object in relation to electrodes of the two capacitances.
DE 10 2008 005 783 B4 shows a capacitive detector as a crash protection system that uses a push-pull measurement bridge to compare the capacitance of two capacitances with one another. One of the capacitances is formed by two electrodes that can be positioned relative to one another, so that a change in their relative interval can be used to generate a signal that warns of crashing.
The disclosure is based on the object of specifying a locating appliance for capacitive detection that does not require calibration in order to attain a high level of measurement accuracy.